It is an old trope in submarine movies. A sonar operator strains to hear things in the ocean but dares not “ping” for fear of giving away the boat’s location. Radar has a similar problem. If you want to find an airplane, for example, you typically send a signal out and wait for it to bounce off the airplane. The downside is that the airplane now knows exactly where your antenna is and, these days, may be carrying missiles to home in on it. In a recent post, [Jehan] explains how radar, like sonar, can be passive.
Even if you aren’t worried about a radar-homing missile taking out your antenna, passive radar has other advantages. You don’t need an expensive transmitter or antenna, a simple SDR can pull it off. You don’t need a license for the frequencies you want to use, either. You are just listening.
Although vapor-compression refrigeration is a simple concept, there are still a lot of details in the implementation of such a system that determines exactly how efficient it is. After making a few of such systems, [Hyperspace Pirate] decided to sit down and create a testing system that allows for testing of many of these parameters.
Some of the major components that determine the coefficient of performance (COP) of a heat pump or similar system include the used refrigerant, as well as the capillary tube diameter or expansion valve design. For the testing in the video three refrigerants are used: R600 (N-Butane), R134a (tetrafluoroethene, AKA Freon) and R290 (propane), with R134a being decidedly illegal in places like the EU. The use of R600 instead of R600A is due to the former allowing for a lower pressure system, which is nice for low-power portable systems.
The test rig has the typical fresh-from-the-scrap-heap look that we’re used to and love from [Hyperspace Pirate], but does exactly what it says on the tin, and is easy for any DIY enthusiast to replicate. Which compressor to pick for a specific refrigerant is also covered in the video, along with oil type and more.
For basic systems you’d use a simple capillary tube, whereas an airconditioner or similarly more complex system would use an adjustable valve design. With the rig you can test the efficiency of different tube diameters, with three sizes available in this version. Unfortunately the electronic expansion valve (EEV) that was going to be used didn’t get a chance to shine due to unforeseen events.
With the R134a and butane a COP of 2.0 – 2.5 was achieved when taking power factor into account, which was reasonable considering a compressor was used that targets R134a. Regardless, if you have ever felt like repurposing that old compressor from a fridge or AC unit, this might be a fun afternoon project.
Kiki bills itself as the “array programming system of unknown origin.” We thought it reminded us of APL which, all by itself, isn’t a bad thing.
The announcement post is decidedly imaginative. However, it is a bit sparse on details. So once you’ve read through it, you’ll want to check out the playground, which is also very artistically styled.
If you explore the top bar, you’ll find the learn button is especially helpful, although the ref and idiom buttons are also useful. Then you’ll find some examples along with a few other interesting tidbits.
There’s a long history of devices originally used for communication being made into computers, with relay switching circuits, vacuum tubes, and transistors being some well-known examples. In a smaller way, pneumatic tubes likewise deserve a place on the list; [soiboi soft], for example, has used pneumatic systems to build actuators, logic systems, and displays, including this latching seven-segment display.
Each segment in the display is made of a cavity behind a silicone sheet; when a vacuum is applied, the front sheet is pulled into the cavity. A vacuum-controlled switch (much like a transistor, as we’ve covered before) connects to the cavity, so that each segment can be latched open or closed. Each segment has two control lines: one to pressurize or depressurize the cavity, and one to control the switch. The overall display has four seven-segment digits, with seven common data lines and four control lines, one for each digit.
The display is built in five layers: the front display membrane, a frame to clamp this in place, the chamber bodies, the membrane which forms the switches, and the control channels. The membranes were cast in silicone using 3D-printed molds, and the other parts were 3D-printed on a glass build plate to get a sufficiently smooth, leak-free surface. As it was, the display used a truly intimidating number of fasteners to ensure airtight connections between the different layers. [soiboi soft] used the display for a clock, so it sits at the front of a 3D-printed enclosure containing an Arduino, a small vacuum pump, and solenoid valves.
This capacity for latching and switching, combined with pneumatic actuators, raises the interesting possibility of purely air-powered robots. It’s even possible to 3D-print pneumatic channels by using a custom nozzle.
Although we can already buy commercial transceiver solutions that allow us to use PCIe devices like GPUs outside of a PC, these use an encapsulating protocol like Thunderbolt rather than straight PCIe. The appeal of [Sylvain Munaut]’s project is thus that it dodges all that and tries to use plain PCIe with off-the-shelf QSFP transceivers.
As explained in the intro, this doesn’t come without a host of compatibility issues, least of all PCIe device detection, side-channel clocking and for PCIe Gen 3 its equalization training feature that falls flat if you try to send it over an SFP link. Fortunately [Eli Billauer] had done much of the leg work already back in 2016, making Gen 2 PCIe work over SFP+.
The test setup involves a Raspberry Pi 5 on a PCIe breakout board and a PCIe card connected to the whole QSFP intermediate link with custom SFP module PCBs for muxing between PCIe edge connector or USB 3.0 connectors to use those cheap crypto miner adapter boards. The fiber is just simple single-mode fiber. Using this a Gen 2 x1 link can be created without too much fuss, demonstrating the basic principle.
Moving this up to Gen 3 will be challenging and will be featured in future videos, involving more custom PCBs. With Gen 5 now becoming standard on mainboards, it would be great to see this project work for Gen 3 – 5 at link sizes of x4 and even x16 so that it might be able to run external GPUs at full bandwidth unlike Thunderbolt.
You probably don’t think about it much, but your PC probably has a TPM or Trusted Platform Module. Windows 11 requires one, and most often, it stores keys to validate your boot process. Most people use it for that, and nothing else. However, it is, in reality, a perfectly good hardware token. It can store secret data in a way that is very difficult to hack. Even you can’t export your own secrets from the TPM. [Remy] shows us how to store your SSH keys right on your TPM device.
Talking with [Tom Nardi] on the podcast this week, he mentioned his favorite kind of hack: the community-developed open-source firmware that can be flashed into a commercial product that has crappy firmware, thus saving it. The example, just for the record, is the CrossPoint open e-book reader firmware that turns a mediocre cheap e-book into something that you can do anything you want with. Very nice!
And that got me thinking about “kinds of hacks” in general. Do we have a classification scheme for the hacks that we see here on Hackaday? For instance, the obvious precursor to many of Tom’s favorite hacks is the breaking-into-the-locked-firmware hack, where a device that didn’t want you loading your own firmware on it is convinced to let you do so. Junk-hacking is probably also a category of its own, where instead of finding your prey on AliExpress, you find it on eBay, or in the alleyway. And the save-it-from-the-landfill repair and renovation hacks are close relatives.
What other broad categories of hacks are we missing? And which are your favorite?
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